Drupal 8 no longer supports upgrading data from Drupal 7 using the database update system (update.php). Instead, Drupal core and contributed modules will provide data migration from Drupal 6 and 7 installations to Drupal 8 installations using a Drupal 8 data migration feature based on the Migrate module.

Minor and patch version upgrades will still use update.php, including (for example):

8.0.0 to 8.0.1

8.0.7 to 8.1.0

8.x-1.0 to 8.x-1.1

Impacts on contributed module developers

Use the migration API instead of hook_update_N() to migrate data to Drupal 8

To upgrade your module's data to Drupal 8 from Drupal 6 or 7, use the Drupal 8 Migration API to give module users a way to migrate the data from a Drupal 6 or 7 site to a newly architected Drupal 8 site. (See https://drupal.org/node/2141805 for an example.) hook_update_N() should only be used for minor version updates (for example, a schema change introduced in 8.x-1.1).

Schema version 8000 is reserved for the minimum core schema version

Previously, hook_update_N000() was used to denote the hook that provided an upgrade from Drupal N - 1 to Drupal N. Since this is no longer supported, the schema version 8000 is now reserved for the minimum installed version of core modules with no updates.

The constant SCHEMA_INSTALLED is replaced with \Drupal::CORE_MINIMUM_SCHEMA_VERSION, which will have a value of 8000 for Drupal 8, 9000 for Drupal 9, etc.

Core modules should begin numbering their minor version update hooks with hook_update_8001().

Contributed modules should begin numbering their minor version update hooks with (e.g.) hook_update_8100() for the 8.x-1.x branch of the module. (See the hook_update_N() API documentation for more information.)

Declaring hook_update_8000() in a module is not allowed and will prevent updates for being run for that module.

Impacts on site owners

It is no longer supported to upgrade a Drupal 7 site to Drupal 8 directly. If you attempt to upgrade a site with a Drupal 7 database to Drupal 8, you will receive a requirements error. To upgrade to Drupal 8, install and configure a new Drupal 8 site mirroring your Drupal 7 site, and then migrate your data using the new Migrate in core functionality once it is complete in an upcoming Drupal 8 release.

Core API changes

Several update helper functions are removed.

update_add_uuids()

update_add_cache_columns()

function update_prepare_stored_includes()

function update_prepare_d8_bootstrap()

function update_prepare_d8_language()

function update_fix_d8_requirements()

function update_variable_get()

function update_variable_set()

function update_variable_del()

function update_variables_to_config()

function update_install_default_config()

function update_variables_to_state()

function _update_8000_entity_get_display()

function _update_8000_entity_get_form_display()

function _update_8003_field_create_field()

function _update_8003_field_create_instance()

function _update_8006_field_write_data_sql()

function _update_7000_node_get_types()

Additionally, update_extra_requirements() is replaced with specific functions update_system_schema_requirements() and update_settings_file_requirements().